Prevent PR-close workflows from ending in action_required when intentionally inapplicable

[Copilot]

Two PR-close workflows were frequently ending with action_required on the same day due to event filters eliminating all runnable work. This change ensures each workflow has an explicit non-error path for ineligible PR-close events.

• Root-cause containment: no-job runs on filtered PR-close events

  • Label Closed PRs could skip its only job when the PR was merged or on copilot/* branches, leaving the run without executable work.
  • PR Description Updater used a top-level workflow if gate that could similarly short-circuit all jobs.

• Workflow hardening: guaranteed executable path

  • Added skip-non-target-prs job to label-closed-prs.yml for merged/Copilot-branch closures so the workflow resolves cleanly instead of surfacing action_required.
  • Removed the top-level if gate from pr-description-caveman.md and moved eligibility checks into prompt logic, where ineligible events call noop and exit intentionally.

• Generated workflow alignment

  • Recompiled pr-description-caveman.lock.yml to reflect the markdown source updates and preserve runtime behavior.

jobs:
  skip-non-target-prs:
    if: github.event.pull_request.merged == true || startsWith(github.event.pull_request.head.ref, 'copilot/')
    steps:
      - run: echo "Skipping Label Closed PRs for merged PRs and Copilot branches."

• Fixes [workflow-health] Label Closed PRs + PR Description Updater — persistent action_required (Jul 25) #47925

[pelikhan]

@copilot resolve the merge conflicts in this pull request